1. One belief is that it originated in Rome when the subsonic plague was raging through Europe. One of the symptoms of the plague was coughing and sneezing,
and it is believed that Pope Gregory VII suggested saying “God bless you”
after a person sneezed in hopes that this prayer would protect them from an otherwise certain death.

2. The expression may have also originated from superstition.
Some people believe that the custom of asking for God’s blessing began
when ancient man thought that the soul was in the form of air and resided in the body’s head. A sneeze, therefore, might accidentally expel the spirit from the body
unless God blessed you and prevented this from occurring.

3. Some ancient cultures also thought that sneezing forced evil spirits out of the body
endangering others because these spirits might now enter their bodies.
The blessing was bestowed to protect both the person sneezed and others around him.

4. The heart was believed to momentarily stop during a sneeze (it doesn’t),
thus the “Bless you!” was uttered either as a supplication for life to return or
as a congratulation upon its successful restart.

Interesting Facts about sneezing :

1. Sneezes are an automatic reflex that can’t be stopped once sneezing starts.
2. Sneezes can travel at a speed of 100-150 miles per hour and the wet spray can radiate five feet.
3. People don’t sneeze when they are asleep because the nerves involved in nerve reflex are also resting.
4. Between 18 and 35% of the population sneezes when exposed to sudden bright light.
5. Some people sneeze when plucking their eyebrows because the nerve endings
in the face are irritated and then fire an impulse that reaches the nasal nerve.